//the method is sending verification code //the country id is concatenated //you can take the country id as user input as well private void sendVerificationCode(String mobile) { PhoneAuthProvider.getInstance().verifyPhoneNumber( "+" + mobile, //phoneNo that is given by user 60, //Timeout Duration TimeUnit.SECONDS, //Unit of Timeout TaskExecutors.MAIN_THREAD, //Work done on main Thread mCallbacks); // OnVerificationStateChangedCallbacks }